(a) Field of the Invention:
The present invention relates to a spiral wound gasket employing carbon/carbon composites of the soft . type, which is used as a pipe fitting etc. for use under high temperature and pressure conditions, and a fabrication method thereof.
(b) Description of the Prior Art:
Spiral wound gaskets of this sort, as disclosed in Japanese Utility Model Laid-Open No. 101253/1981 (Applicant: Japan Pillar Industries Co.) by way of example, employ a tape made of asbestos or expanded graphite as a filler and have a structure of a metal strip having a V-shaped cross section, made of aluminum or copper, and said tape are laminated together in the longitudinal direction and wound spirally.
However, conventional spiral wound gaskets involve problems as described below.
With a spiral wound gasket employing a tape made of asbestos as a filler, the asbestos is apt to generate a large volume of dust during handling, raising such a sanitary problem that persons who have inhaled the dust for a long period of time are liable to get cancer of the lung. In addition, the elution of the halogen components in the asbestos into the fluid being sealed necessitates a sufficient anti-corrosion plan to be established. Moreover, due to the insufficient elasticity of the asbestos, its sealing performance is not always satisfactory.
On the other hand, with a spiral wound gasket employing an expanded graphite tape as a filler, the elution of the halogen components and the carcinogenic problem are avoided and the sealing performance is also improved. Nevertheless, it is necessary to further improve the sealing performance of the gasket in order to use the gasket under higher pressure conditions, keeping step with the recent development of technology. Since the expanded graphite tape is susceptible to breakage by nature, it occasionably breaks when the tape and the metal strip in a pile are wound by application of a tensile force. Further, the tape often breaks when it is bent. Hence it is necessary to improve the strength of the tape.